To start your X-server automatically on the system start-up and display a graphical login prompt, you have to change (as root) just one character in the file /etc/inittab .  This file specifies something like:

id:3:initdefault:

Change it to

id:5:initdefault:

This sets up the default runlevel to 5, which is X-Windows. The meaning of the different runlevels is explained in the same /etc/inittab file :

0 - halt (Do NOT set initdefault to this)
1 - Single user mode
2 - Multiuser, without NFS (The same as 3, if you do not have networking)
3 - Full multiuser mode
4 - unused
5 - X11
6 - reboot (Do NOT set initdefault to this)

You can change the runlevel from the command line. E.g., this command (has to be executed as root):

init 6

will reboot your computer, while the following command would switch your computer to a single-user mode:

init 1

To find out which runlevel I am currently at, I use the command runlevel.

How do I install kde (e.g., on RedHat 5.2)?

RedHat 5.2 does not install kde by default because at the time of the RH5.2 release there was a problem with the license for a library that the kde uses. Otherwise, kde is a very good GUI, the library license problem is now solved, and the RedHats 6.0 up include kde (alongside the more ornamental GNOME). Still, the kde binaries are on your RedHat 5.2 CDs, you just have to install them yourself. (If you don't have the CDs, you can download the binaries from the kde site on the Internet.)

First check if your X-server works by executing:

xinit

[The X-server is a bare-bone X-windows system, without a "Windows Manager." You can execute your X-windows programs from here by typing the program name (with leading ./ or full path) in the X-terminal window, but you will not be able to move or resize the windows, add icons, etc.]

You can exit your X-server by typing exit in the X-terminal window, or pressing <Ctrl><Alt><Bkspace> to kill the X-windows server. (The last solution is perfect should your windows ever hang-don't reboot in such a case.) If your X-server does not work, see the next answer.

Now, login as root. Mount the RH5.2 CD:

mount /mnt/cdrom

Go to the proper directory:

cd /mnt/cdrom/kde/distribution/RedHat/i386/binary

It is useful to use the command line autocompletion (press Tab) when typing long paths or filenames.

Read the README file:

cat README-2rh51-rpms | more

Use the rpm  "RedHat Package Manager" to install the necessary packages

rpm -iv packagename

The packages have filenames ending with .rpm. First install the qt libraries, then kde support, then kde libs, then kde base. If you choose the wrong order, the dependency check will fail and the package will not install (rpm will issue a message). This is not serious, just re-install the required package first, and then try the next package again. After you are done with the base, you may want to install all other packages for kde (util, admin, network, games, graphics, multimedia)--they are not big, so you may consider installing them all. Finally, just to make sure that you installed everything type:

rpm -ivh  *.rpm

The options "vh" print some extra info. You will get some messages like "the package is already installed" If there is more than a screenful of them, you can scroll back using <Shift><PgUp>. If you really don't like the command-line-based rpm package manager, you may install the same packages using a GUI front to rpm called glint (available only in RH5.2). Just type "glint" in the X-windows terminal.

Now tell your system that kde is to be your default X-windows manager. In the user home directory, create an   .Xclients file:

pico .Xclients

which contains just one line:

/opt/kde/bin/startkde

Type in the line and save the file. (Adjust the line as required so the location of the startkde file is correct.) Now, make the file executable to all users:

chmod a+x .Xclients

Check if the permissions were changed:

ls -l .Xclients

[Files with a dot at the beginning are not displayed by a regular ls command, there are something like hidden files under DOS. You must use its name or ls -a  .]

If you created the file as root not the user, change the owner and the group of the file to the proper user:

chown user_name .Xclients
chgrp user_name .Xclients

That's it. Now typing startx should start your X-server with the kde as the windows manager.